This invention generally relates to actuators for bringing gears into meshing engagement. More particularly, this invention relates to such actuators which find particular, but not exclusive, utility as part of a power takeoff device attachable to the transmission of a vehicle.
The mechanical arts have universally had to face the problem of how to successfully bring two rotatable gears, selectively, into and out of gear meshing engagement, such that both gears when engaged will then operate (rotate) together when desired, to do some form of useful work, normally one gear driving the other. One environment in which this problem has had to be faced and solved if the device is to be commercially acceptable and safe to employ, is in the well known art of power takeoff devices (herein referred to by their industry acronym xe2x80x9cPTO""sxe2x80x9d). PTO""s have found commercial uses in a wide variety of areas, such as in the vehicular arts where the PTO is attached to the transmission of the vehicle for translating the power of the engine into the rotation of a shaft for doing useful work auxiliary to the vehicle itself (e.g. operating a hydraulic pump for raising and lowering a dump truck bed, compacting a garbage compactor, and the like).
In order to perform their assigned tasks PTO""s are generally formed of an arrangement of gears associated with an output shaft and a mechanism for selectively engaging and disengaging one of the gears in the PTO with another gear in the PTO which is constantly engaged with a corresponding gear in, for example, the transmission of the vehicle. Since it is highly undesirable in most instances to have the PTO output shaft constantly rotating, various devices have been developed in the art for effecting, selectively, the aforesaid engagement and disengagement, whether the PTO be attached to a vehicle (truck, tractor, etc.) or to some other power driven device (e.g. stationary engine rig).
In the normal situation experienced in the PTO art, meshing engagement and/or disengagement of the gear(s) of the PTO is generally achieved by axially displacing the operative PTO gear with respect to its input gear. Axial displacement for meshing engagement or disengagement (with the gears at rest, i.e., without synchronization) is usually achieved by means-of mechanical actuators, which may be pneumatically or electrically (and less often manually) operated.
There are certain known drawbacks to the actuators currently in use. For example, certain electrically operated actuators employ solenoids which are rather large and space consuming and provide a limited amount of actuation travel. Certain other electrical actuators use electric motors which actuate screw transmissions having or requiring bearing recirculation and/or which are operated by complex electronic control circuits. For example, to mesh the gears requires a xe2x80x9cdosedxe2x80x9d sequential execution having a very precise succession of operative phases (or steps). In certain prior art devices, furthermore, the axially movable gear (wheel) must be brought into contact with an axially fixed gear and thereafter maintained in pressed contact against the fixed gear until, by the effect of relative rotation, the gear teeth of the two gear wheels are caused to coincide (i.e., enter into the inter-gear spaces of the other) thus achieving operative meshing engagement. Moreover, in order to carry out the above-described phases (steps), special operations have to be put in place. For example, the use of a screw transmission with,bearing circulation may have to be employed, as well as a fine and sophisticated adjustment of the electric motor through the use of a complex and expensive control circuit employed to actuate it.
In another known type of actuator, an electric motor is employed to draw in, by rotation and usually with an axially slidable, geared coupling, an axially-slidable intermediate rotating body. In such a device a nonrotatable screw coupled with a lead screw bored coaxially into the intermediate body, functions as the moving part of the actuator. In this configuration, the positioning of the intermediate body in the direction of mesh is not rigid. Rather it is governed or controlled by an intermediately located, specially calibrated spring. If meshing is accomplished, the screw in the intermediate body becomes immediately locked and the body acts rigidly on a slidable rod to directly command an appropriate xe2x80x9cendrunxe2x80x9d switch to actuate and stop the motor. If meshing is not achieved (i.e., is messed), the intermediate body is caused to retreat from the meshed position. When and if complete meshing is achieved, the screw head retreats with respect to the intermediate body, eventually terminating travel by acting directly on another xe2x80x9cendrunxe2x80x9d switch which, again, deactivates the electric motor.
The drawbacks to these known devices are known and generally include, as their main drawback, the fact that the alignment of the parts for actuating the switches must be of such preciseness that repeatability becomes unreliable.
It is apparent from the above that there exists a need in the art for an actuator which overcomes or at least minimizes the above-described drawbacks endemic to prior actuators, as above-described. Preferably, such an actuator would also be simple to operate, economical in its simplicity of parts, and yet reliable in its operation. It is a purpose of this invention to fulfill this and other needs in the art apparent to the skilled artisan once given the following disclosure.
Generally speaking this invention fulfills the above needs in the art by providing:
an actuator comprising a frame and a rotatable intermediate body freely rotatable with respect to the frame and provided with an externally toothed gear wheel meshingly engaged with a pinion fixed to an end of a shaft of an electric motor, the rotatable intermediate body being further provided with a lead screw area extending therewithin and arranged coaxially thereto; the intermediate body being capable of moving axially in either direction over a predetermined distance which distance is sufficiently limited in length so as to maintain the meshing engagement between the externally toothed wheel and the pinion; the actuator further comprising a spring operatively located coaxially between the frame and the intermediate body, a screw shaft member coaxially and screwably coupled with the lead screw area and which has a first end connected to the frame by a coupling member which prevents relative rotation while allowing free axial movement, a switch means for operating the electric motor, the switch means being actuatable by the intermediate body upon relative movement of the intermediate body. In preferred embodiments the intermediate body is not mechanically rigidly connected to the switch means.
In certain particularly preferred embodiments of this invention, the aforesaid actuator is operatively coupled to a power takeoff device for selectively engaging and disengaging the input gear of the power takeoff device with its output shaft.